2011/07/03

80 years too late - but still an interesting idea (at least to me)

.

Back in WW1 the German infantry needed something to take out machine gun nests and pillboxes at a distance. Indirect fires were too inaccurate, bullet fire was unsatisfactory, bazookas didn't exist yet, almost no tanks were in the inventory, flamethrower range was unsatisfactory and light field cannons were too unwieldy. Mountain guns and lightened field cannons were eventually pressed into service as a stop-gap solution.

The inter-war years answer for this requirement was the infantry gun (especially the light version). It was a kind of cheaper mountain gun (not meant to be fully disassembled), had a protective shield, lobbed a (slow) 75 mm HE shell (calibres varied internationally; 47 to 76.2 mm calibres were used for the light infantry gun concept; 47 mm was an improvisation) and most importantly: It was crew-mobile.

An infantry gun wasn't portable, but its crew was able to manoeuvre with it on a battlefield, and that satisfied (till enough tanks were available/affordable).

The Brandt system for simple, yet effective infantry mortars was not fully adopted till the early 30's, so these infantry guns were also meant to serve as indirect fire guns of infantry regiments, too. Most missions could actually be met with indirect fire, but infantry gun indirect fire was a bit different than normal mortar or artillery indirect fire. They were usually quite close to the target and their platoon leader was the forward observer - often times there was only a single interruption of the line of sight that protected the crew against spotting and counterfire. A low muzzle velocity and corresponding high trajectory of the shell helped to overshoot this one concealing object. A gun crew close to its forward observer and both being part of the same platoon or company was a huge advantage over normal indirect fire support. Radios were still rare, field telephone cables couldn't be laid over long distance quickly and separating both organisationally would have been an invitation for Clausewitzian friction.

The First World War spawned another requirement, too: The requirement for a dedicated anti-tank gun. The early tanks were basically slowly moving pillboxes, and posed quite similar problems.

Anti-tank rifles (interesting story) and anti-tank machine guns were unsatisfactory (rifle: not enough effective range and not much effect, machine gun: not enough effective range). A gun, about as light and manoeuvrable as an infantry gun, could meet the anti-tank requirement. It couldn't do so with the slow 75 mm high explosive shell, though. Early (pre-'38) tanks had thin armour, but they became faster. A higher muzzle velocity was desirable in order to actually hit the target at long ranges.

It would have been perfect if the same carriage could be used as for infantry guns, but that was impossible (or was it?): The carriage was only able to absorb a certain amount of recoil, especially at low gun elevation angles.

You can have a relatively heavy high explosive shell, but that restricts muzzle velocity. or you could choose a high muzzle velocity for short time of flight and good accuracy - but that limits the shell weight.

Barrel length created quite the same trade-off dilemma: A long barrel enables a high muzzle velocity, but it would become too heavy if built with a large calibre for suitability for high explosive shells.
75 mm was widely regarded as a good minimum calibre for high explosive shells; anything smaller was considered to be or rather disappointing effect.

The inter-war choice was eventually for 65 to 76.2 mm for light infantry guns (often based on old, suboptimal calibres and guns) and 37 to 47 mm for light anti-tank guns.

There were actually three similar 37 mm calibres in Germany; army AT gun (37 x 249, 192 kJ), Luftwaffe AA gun (37 x 264, 210 kJ) and navy AA gun (37 x 381R, 372 kJ).
The naval gun was least famous, least successful and most powerful in regard to muzzle energy. With hindsight, the naval 37 mm cartridge or the Swedish 40 mm AA gun cartridge would have been better choices (but only marginally better) than the historical 37 mm light AT gun cartridge. Even a standardisation between army AT gun and air force AA gun would have been a good idea.

Mountain guns could be assembled and disassembled, even infantry guns had a removable sight. Why not create a convertible gun?

The same carriage could be used for an infantry gun calibre 75 mm and an anti-tank gun calibre 37 mm (naval or at least air force calibre; muzzle brake if necessary). All you needed to do was to remove one gun (barrel+breech+sights) and insert the other one. This exchange could have been quite quick (1-2 min).

Such a gun could have busted above-surface fortifications in direct fire (75 mm HE), provided indirect fire support (75 mm HE, SMK) and defeated lightly armoured tanks (37 mm AP). All this was necessary for infantry regiments (if not battalions!). Many reports about tactical engagements in WW2 mention that 1-2 infantry guns, 1-2 light AT guns, 1-3 mortars were added to company or battalion defensive positions. Their effectiveness was badly needed if infantry had to fight on open terrain.
A convertible gun would have been able to match all three roles; two near-perfectly, one satisfactorily (81.4 mm mortar HE was of course more effective than 75 mm gun shell HE). The net result would have been less logistic troubles, easier positioning and overall greater firepower.

- - - - -

It would have become outclassed as indirect fire weapon by about the late 30's because of the availability of decent infantry mortars of Brandt system (no more than historical infantry guns were outclassed, though).

It would have become obsolete as anti-tank weapon in 1938-1942 because of increased armour plate strengths (but that could have been partially compensated for with a squeezebore attachment such as the Littlejohn adaptor or a conical barrel - as long as tungsten is available for the penetrator). The historical light AT guns eventually met this fate.

It would have become inferior (but still at least affordable) as infantry direct fire support weapon with the rise of assault guns and CS ("close support") tanks by about 1940. This didn't push the historical light infantry guns out of service, though; they were numerous, but tanks were always in short supply in most armies.

Yet, it would have fared better than the historical light infantry and anti-tank guns:

Its versatility and its ability to exploit shaped charge shells (penetration in 1942 ~ calibre = 75 mm) in the AT role would have kept it more useful. Light AT guns were kept in front-lie service till about '43 and light infantry guns were kept in front-line service till '45, some were even used post-WW2.

Later on, the same carriage could easily have been converted with a smoothbore high-low pressure gun of 75 mm calibre to regain its initial effectiveness in all roles with only one barrel. A 81.4 mm calibre gun with this principle was eventually produced and used with a 50 mm AT gun carriage.

81.4 mm PAW 800 a.k.a. PWK 8H63

The final obsolescence would have been reached sometime in the 1950's when tanks (with their ability to carry a powerful gun) were available for almost all army units and became rather invulnerable to frontal hits with even then-modern 75 mm shaped charge warheads.

- - - - -

Well, what kept such a convertible gun from being introduced?

I guess there are several reasons. Few armies valued both AT guns and infantry guns highly, and those that did were either in a bad shape during the mid-30's, had an unsuitable doctrine or were in a hurried rearmament.
AT guns were furthermore organised separately from infantry guns; the German AT doctrine preferred highly mobile AT gun batteries, but wartime necessities forced many AT guns into close and quasi-permanent cooperation with infantry units. You cannot protect the infantry against a tank attack with any satisfactory reliability if don't accompany it. The fast-mover AT doctrine was satisfactory against successful tank breakthroughs (especially once it was applied to the tank destroyers instead of towed guns), not so much in regard to preventing said breakthrough.

Light convertible battalion guns would probably have been highly successful (production-wise) if military technology had taken a break in the mid-30's instead of moving forward in great haste.

S O

edit 2013-04:

Same idea, actually attempted soon after WWI, but with too feeble calibres.

41 comments:

Convertible and even dual barral guns were actually developed in the interwar years (Czechoslovakia, Belgium, Sweden afaIk).

Null-Hypothesis:Those did not translate into service guns because the idea is unpractical.

First of all because both functions were in need in combat (Even if no enemy tanks were yet encountered, AT-guns had to stand prepared, preferably in ambush position, as moving them into position once tanks approached was neither timely nor save). Second, because the battlefield position of an IG is less than optimal for AT-use and the position of an AT-gun is suicidal for IG-use. Furthermore bot AT-guns and IG were higly weight sensitve systems, adding an est. 40% in weight for an exchange barrel was likely regarded a big disadvantage. IG-fire from an AT-position would have compromised the ambush position (Lauerstellung). Last but not least, if you are producing 4digit numbers of IG there is a benefit in going for the low cost box type carriage and if you are producing 5digit numbers of Pak you might want to pass on an expensive two zone elevation mechanism. The economics of mass armies does not favour modularity.

When the 12 cm GrW was introduced in the Wehrmacht inventory the IG became obsolete as their main advantage (higher range than GrW 34) was no longer needed.

At least some of them were also discussed in contemporary military journals.

As refered to cost savings by modularity, I assume this only applies if the total number of systems can be reduced (?), which I doubt is possible.

In regard to pros and cons, my conclusion so far is, that because of the factory mentioned previously, most of the pros dont work out tactically (you will have to ad significant weight to your IG and some of your Pak, Positioning). There might be an opportunity in adjusting your force to a more tank/more infantry heavy OPFOR, but because of the relatively low number of IGs (you cannot gain many additional Paks) and their niche application (you cannot gain much by converting Paks to additional IGs), I do not expect much benefit.

Interesting link, but none of the guns described there fits to this conversion gun idea well.

Your argumentation is not as conclusive as you seem to think, for there were many successful multi-role guns; especially the ZIS-3 and the 8,8 cm Flak. Their success would have been largely impossible if your first comment's arguments were decisive.

Let's look at the key disagreement; did armies need AT guns and IGs at the same time, without being able to adapt them to the other role by reconfiguring and repositioning?

Context: Defensive lines were several km deep, and attacks - even of armoured forces - required hours if not a full day to penetrate them. All but the most forward units had apparently enough time for adaption of their guns to their needs.

"Interesting link, but none of the guns described there fits to this conversion gun idea well."

why?

As this is gonna boil down to our Pak/FK vs. Pak and FH debatte: I am still not convinced that you can dispense lightly with indirect fires in presence of a major tank attack.

Lets qualify the benefits of convertible IGs: Taken all Paks are distributet equally you gain 20% AT firepower (6Pak/IG, 24 Pak in one regimental area). But normally the divisional pak would form a Schwerpunkt or be deployed on notice to the most tank threadened regimental area giving up to 48 Pak there. As concentration of IG in this scope is impossible (horsedrawn, regimental weapons), you gain only an 11% increase. All this assuming that all IGs are converted, which would propably not happen.

In non Schwerpunkt regimental areas you might gain up to 33% increase, but those areas are secondary for a reason. Propably they have more broken terrain, increasing the need for indirect fire to plug up the fires plan.

Even if this equations under certain tactical circumstances amounts to a favourable outcome, there is still doubt, that it is worth the effort economically, training-wise. Not to mention the every-day tactical problems that come with an now essentially 600 kg IG (less ammunition*, exhaustion of horses, cross country mobility).

*) The supply of ammunition is another problem, assuming that a convertible IG could only be equipped with a very small amount of ready AT-shells. The problem of conversion is therefore exacerbated by the necessity of timely resupply of AT-ammunition to the converted gun.

"I am still not convinced that you can dispense lightly with indirect fires in presence of a major tank attack."

You assume too much. For one, many armies hadn't even light infantry guns, so their loss was proven to be acceptable.Second, they would not be the only indirect fire asset; especially in a Schwerpunkt, divisional if not corps-coordinated artillery fires would dominate.

Third, I glanced at the topic of fast AT vs. organic AT. Convertibles would be organic AT, while there would still be divisional AT units (or light field cannon batteries with secondary AT role ~ ZIS-3).

The organic regimental weapons were meant for reliable support independent of a higher HQ's favours. The convertible gun wouldn't change that.

Finally, even a (possibly) 11-33% increase is a lot, as is an increase in IG firepower over a mixed AT/IG inventory. Improvements are often incremental, but they are still improvements.

The only disadvantage of the convertible concept appears when you assume that an army meets a situation that demands usually very much of one gun type and has actually correctly prepared for this.This match did not exist historically. No force focused on IGs, and those which focused on AT and had no IGs did lack the IG firepower.

- - - - -Your link showed guns with two barrels in one carriage or with small calibre barrel being mounted into a larger calibre stub barrel. Neither would keep the weight down as much or achieve the firepower/weight ratio of the convertible gun. Those concepts were technically very different.

In regard to the subcaliber barrels I dont see significant problems vis-a-vis a detach-large-caliber-barrel-attach-small-caliber-barrel-solution. The only drawback I can think of is the increased weight in AT-mode if man handled. Conversion time might be shorter, as the subcaliber barrel is only to be attached/detached, without need for detaching/reattaching the large caliber barrel. The added weight of the large caliber barrel might even be beneficial to compensate for the higher muzzle energy of an AT-shot? The dual barrel designs are nuts, I agree.

Could you comment on the ammunition issue, the more I think about it, the more it seems like a knock-out argument against convertible guns.

Even if other armies did not employ IGs, this is no prove, that IG firepower is of no value or can be dismissed easily. Take a look at the RKKA Infantry Regiment of 9 medium mortars per battailon, regimental IGs AND heavy mortars. Therefor the above made consideration applies. Indirect fires are of high value as tanks tend to suppresses (even by their presence alone) or destroy direct fire means, responsive infantry indirect fire is of even higher value.

In historical context the IG 18 was developed as the sole infantry indirect fire Weapon in the Regiment, replacing the WW1 Minenwerfer. The case for a convertible gun then (1920s) would have been even harder to make. At least its design was a preexisting condition in the 1930s. As it was put into production one would have had to argue for a new design development. If one looks at all available options, not having IGs at all and employing heavy GrW (a Brandt model was in production 1935, the Wehrmacht could have improved on its NbW 35 design) as regimental Artillery would have been the most promising solution then. Freed resources (a GrW 42 cost only 1/5 of an IG 18, uses less crew and horse) could then be employed otherwise.

The cost of a gun proved to be of lesser concern than its manning requirements and towing requirements during the war. Such a convertible gun would still cost less than 10% as much as a medium tank.

A quick insert barrel would almost certainly have accuracy and dispersion issues - and it would probably only fit well in new stub barrels because of the barrel's wear.

The ammo issue is not really an issue. Anti-tank defences fired a few dozen shots in a battle at most. Neither they nor their opponents could survive longer than that. 37 mm ammo was not very heavy or bulky. Imagine five such clips;http://preview.tinyurl.com/6dckbh2

You would need additional crew to man 2 weapons instead of one. But that is a problem only if you assume, that you would not need the firepower of both weapons. Calculated on firepower, comparing 2 convertible guns (2 x 8 men) and 1 Pak (6 men) plus 1 heavy GrW (8 men) manpower consideration would still favour the second option.

Cannot say much about the technical issues, but I assume that those engineers did their thinking.

Regarding the ammunition question: One Pak had a first line ammunition supply (contained in the towing vehicle) of 180 cartridges. some 40% of those would have been HE, which would not be used by a convertible gun. A cartridge weight of 1.32 kg adds up to 142 kg of ammunition.

An IG had a first line ammunition supply of 120 grenades, some 720 kg. Therefore a weight neutral solution would result in a 20% reduction of HE ammunition. (Note that the weight of the AT-barrel is still not accounted for.) Even if only 50 AT cartridges been carried, some 10% of HE ammunition had to be discarded. This is an issue, allthough definitly no knock-out argument, I admit.

1). Modularity adds complication: If we make a necessity of changing the function of an artillery piece from a rather large and low-velocity piece to a high velocity direct-fire weapon, we have to design for both functions in one chassis. This will add weight in both a physical sense as well a mental sense, this "weight" (the anchoring effect of a sunk cost) limits us in finding other solutions if this one does not work. Other complications come about from simply having the wrong parts at the wrong place and time, now you have to keep track of both two separate barrels and ammo chains and keep sufficient quantities of both , in the same place...this is difficult enough with professional forces, I would think this task would be impossible with conscript or hastily raised forces.

The infantry gun has not completely died, but depending the armed force in question has not fully seen the necessity of the piece, the Russian 2A70 100mm/L18 being a prime example of an infantry gun/rifled mortar ( and if you do not believe me, look at the velocity of the 2A70 and the U.S. M30 107mm mortar). Currently most other forces do not see the necessity of this type of weapon, instead using vastly more expensive platforms to deliver the same firepower (SDB and aircraft, or organic ATGMs).

Combined weapons and precision stand-off weaponry kind of voided such a requirement as you describe.

But what is related and interesting: The recoilless rifle sees a comeback in infantry combat! And not only in the SMAW hybrid and similar systems, but the real, old fashioned M67. And the reason is the large variety of ammo it can launch, and that for drawn-out engagements the barrel solution is weight-wise superior to the rocket solution.

The conscript forces of the 30's were rather competent and often assigned to missions that would nowadays be given to special forces.Conscription was 2-3 years at that time, and it takes only half a year to train men to high competence in enlisted jobs. It's about training quality and intensity, not about "professional" or conscript.

The carriages were not very different; one dispensed with most traverse in favour of elevation - that's the whole difference. The combination of good elevation and good traverse at low weight was easily possible. Almost all alter light infantry gun designs including the mountain, airborne and export development of the leIG 18 had a split trail. Same with most mountain guns.The leIG 18 had a simple trail because it was an old-fashioned design and the pure infantry support role did usually not necessitate a good gun traverse.

I just wanted to add that the Pak 36 has also been used, late in the war, as a direct fire support weapon, mounted on the SdKfz 250 (it was the model 250/10).

Regarding the topic, I think the german army in the 30's was trying to increase the numbers in their equipment. Fielding N light infantry guns and N AT guns was better than fielding N x1,5 modular systems.

My personal view on this is akin to the limitations of the Leatherman : it's better to have separate pliers and screwdriver than both in one tool (for the moment when you need to hold something with the pliers so you can unscrew a part of it...)

Combined weapons and precision stand-off weaponry kind of voided such a requirement as you describe.

But what is related and interesting: The recoilless rifle sees a comeback in infantry combat! And not only in the SMAW hybrid and similar systems, but the real, old fashioned M67. And the reason is the large variety of ammo it can launch, and that for drawn-out engagements the barrel solution is weight-wise superior to the rocket solution.

The reason we are seeing the 90mm recoilless rifles come out of the woodwork is the simple fact that NATO forces have nothing else that can economically fill that void. ATGMs are expensive but accurate, aircraft are not organic to the unit and may not be there when you need them, RPGs are made in another country; simply put the M67 is the only thing on the shelf. A real infantry gun (M98 Howtar, 2A70, 10 cm Nebelwerfer 40) would confer better range, indirect fire capability, and less signature when firing)

The conscript forces of the 30's were rather competent and often assigned to missions that would nowadays be given to special forces. Conscription was 2-3 years at that time, and it takes only half a year to train men to high competence in enlisted jobs. It's about training quality and intensity, not about "professional" or conscript.

What if you do not have the 6 months to train conscripts to a competent level? Engineering competence through specialization will yield benefits in this situation by concentrating training to the task at hand, decreasing time to deploy which will increase mass on the field (assuming unlimited manpower). I know this feels much like an attritionist mindset, but it is a viable solution. Tragically the engineering of NATO forces does not lend itself to this kind of rapid enlargement ( I would hate to be the NATO unit that requests 90mm ammo and gets field gun ammo for my M67s)

"The combination of good elevation and good traverse at low weight was easily possible. Almost all alter light infantry gun designs including the mountain, airborne and export development of the leIG 18 had a split trail."

All german IG designs with split trail carriage did cut back on elevation, restricting it to 43 degree (IG L/13) or even 24 degree (IG former Pak 37). High angle fire was an indispensable feature of an IG, allowing it to engage targets close to ones own troops. Mountain guns (Geb. G. 36) had almost twice the weight of an IG 18. They also used muzzle breaks (thereby increasing the signature of the gun when firing), to allow for less robust carriages.

The Gebirgsinfanteriegeschütz 18 was 10% heavier even though it lacked a gun shield. For perspective: the gun shield of a Flak 38 weighted 120 kg. Propable weight increase of over 25% due to split trail carriage. (I dont assume some butterfly screws and quick fasteners for disassembly add much weight)

The para version of the IG 18 did not have a gun shield and only used small wheels, propably inadequate for more than man drawn transport. It came out 75 kg lighter than the standard IG 18. I assume at least 10-15% weight increase at least (some 20 kg per wheel + 100 kg for the gun shield?).

The Belgian Canon de 76 mm FRC had a ballistic coefficent (Eo/M) of only 244, the IG 18 reached 330. It lacked a gun shield too.

The problem with split trail and high elevation is not if it is possible to design such a gun, but its added weight, complexity and costs.

"added complexity" is hardly a correct description for a split trail. A simple trail needs to be hollowed to allow for upper angle group fire (recoiling barrel), thus it's no 100% simple design either.A split trail may end up requiring less machining and joints due to the use of simple steel tubes.

I do not have the engineering degree to account for how much complexity goes up, but I guess it is obvious it does so.

If you scroll through some military journals of the time you will find, that convertible and dual purpose guns were definitely looked upon with keen interest. This is no story of some ignorant military establishment shunning on an ingenius idea. So I assume there have been some serious technical and/or tactical flaws in the idea of a convertible Pak/IG. Some of them were mentioned here.

Very interesting idea, sven. Reminds me of the XM307 acsw 25mm grenade machine gun, which could be field converted into a regular 50 cal XM312 machine gun in the same minus 2 minute time. I actually still see the need for such an infantry gun, especially in urban warfare (40mm grenades barely make a dent in reinforced concrete), and the 37mm anti-tank gun could still be useful for destroying any non-MBT armored targets. It beats using a 40,000$ javelin missile, or even a 1500$ AT4, in cost effectiveness.

Do you really think a unit could have dispensed with the curved trajectory provided by the mortars, though? Sure, with the infantry gun, you get a quicker response for fire support, a higher probability of first round hit, and much streamlined logistics, but should it really replace all of the divisions 81mm mortars? Mind, the explosive filling for the two shells would be the same (the mortar rounds fins steals from its proportion of payload).

Infantry and AT guns had different job profiles than mortars. Mortars did eventually replace the infantry gun, but that happened only after assault guns and even bazooka-type weapons had taken over much of the direct fire role.

Nowadays a proper bazooka-type weapon (such as the famous M3 Carl Gustaf or the less famous LRAC F.1) is essentially the successor of such a convertible gun concept in all direct fire applications.We overemphasized their AT role during the Cold War, of course.

Have a look at Panzerfaust and Panzerschreck production figures; almost all of these munitions were either never expended or expended on a soft target (including buildings).

Back in '39, a convertible gun could have replaced IGs and ATGs at infantry regiment and battalion level, with light field cannons as brigade/divisional light field arty + 'Pakriegel' AT force.Mortars would have had parallel roles. Light ones (60mm) for companies and long range ones (more than the then usual 81.4 mm calibre's 3 km) for battalions/regiments. The Russians had a great 107 mm mountain mortar and the Stokes-Brandt 60 mm was fine as well.

I never really liked the 81.4 mm calibre. Its range was too small for a Bn mortar and its ammo too heavy for supporting infantry on the move without vehicle or animal support. Somehow the British fell in love with this compromise and standardised completely on it, but I don't get why.

1) IGs were only rarely expected to use direct fire even in the interwar period. Even the minuscule french 37mm IGs! When combat experience tickled in, the german AVI saw them only as slightly more accurate and slightly more far reaching mortars. Direct fire with IGs was a waste of time, against any target without heavy overhead cover (fire at apertures needed), as the gun had to be brought into position first.

2) 81mm Mortars were used because it is the largest calibre that can be broken down into parts one man could carry. (see, no stupid, senile, traditionalist burocrat) Lighter mortars lack penetrative ability (some 30 cm of soil + wooden beams for 81mm grenades). Loosing either capability would be a seriously impediment. First would deny the ability to follow the infantry in the zone swept by direct enemy fire, thereby making the mortar just another artillery piece (under battalion control at least).* Second would make the mortar ineffective against those targets it was explicitly designed to engage.A Range of 3km is enough for most situations. To see targets beyond would normaly necessitate occupation of other positions for the OP (similar to artillery OPs ;) ). The weight of ammunition is acceptable; one or two ammunition carrier could transport the amount necessary for one fire mission (usually a point target). On defense and for the initial stage of a deliberate assault ammo is stockpiled anyway. On the march carts were used (even 60mm ammo cannot be hauled by men for combat marches without a prohibitive increase in combat load).

*) spread of radio coms, fire direction computers and finaly GPS made this consideration somewhat obsolete.

3) The configuration of mortars you envision does not fit the overall tactical infantry doctrine of the Wehrmacht (nor the RKKA). The assignment of basic combat tasks was very uneven between platoon/bataillon and company, with the later being more of a coordination and communication hub for those units that actually organized the fighting. Furthermore the permanent employment of weapons that cannot maneuver in the zone of enemy direct fire, denies the bataillon to push to the depth in presence of enemy pockets of resistance, without total loss of a significant component of its combat power.

It's well-known that destructive fires were very ammunition-intensive. The penetration capability was thus of marginal utility - especially in combination with the foot mobility. A 81.4 mm mortar bomb weighs several kg. You cannot transport much ammo this way, especially after half your mortar team is extremely heavily laden with the weapon itself.

So basically neither the advantage of 81.4 mm over 60 mm nor the advantage of 81.4mm over 107 mm was as relevant in practice as on paper.

By the way; direct IG firepower was often an important part in defensive plans.

The amount of ammo required depends on how close you can get: Firing from 500 m a machinegun position with overhead cover can be destroyed with 11-15 rounds (depending on the charge you use). From 1000m you need ~27 rounds. (2000 = ~90 rounds, 3000 = ~150 rounds) Of course only 81mm mortars are able to follow this close behind the infantry and still bring a significant penetrative ability.

"By the way; direct IG firepower was often an important part in defensive plans."

... in the russo-japanese war and early WW1 until MGs were available in high numbers. Maybe you mistook masked positions?

Machine guns are no full substitute for 75 mm HE. A light IG in a company hedgehog position was quite common.

Even eleven 81.4 mm mortar bombs (and the real figure 'depends' on much) already weigh about 40-45 kg + about 5 kg for transportation cases. That's enough to completely occupy two carbine-armed porters.Add in a minimum of smoke and Illum, the mortar components, the fire control equipment/radio/telephone and some self-defence items and you end up with the capability to destroy a single light field bunker per 81 mm mortar squad.

The real strength of such mortar bombs is versatility and their frag effect (the latter due to the angle of descent). Their utility in destroying protected targets is marginal. That's why 60 mm suffices and sufficed for the purpose; it's more efficient in frag area per kilogram.Mortars on a higher level (Bn, Rgt) require more range than 81.4 mm mortars offered, and thus my preference for stuff like the Russian 107 mm mountain mortar or today's 98 mm models. 120 mm rules if enough cargo and guided mortar bombs are available, of course.

1) even if each mortar team only kills one machine gun position, this amounts to something in a defensive zone usually attacked by one bataillon, especially after artillery thinned out the enemy system of fires.

2) what will 11 or even 27 grenades gain in suppression compared to the lasting effect of the enemy machine gun destroyed? Or 22-54 of the 60mm model? The mortar team would be occupied for a longer time. Propably blasting away on an enemy position long deserted for an alternative one. Note that heavy machine guns could cover predetermined areas with fire without the crew being exposed for more than reloading the gun.

3) the ammo of a mortar team was constantly replenished by the ammo carriers from a not so far ammo dump and additional carriers could be employed if needed.

"A light IG in a company hedgehog position was quite common."

Check if it is employed from a masked position. IG fire has an excessive signature, any gun firing in the open for more than some minutes would propably come under heavy fire.

I subscribe to your comments about range for the period way after the war. Around WW2 81mm mortars had their place for the reasons I already mentioned and 120mm mortars were good for regimental artillery or even as a supplement to the bataillon mortar pool. I dont like company mortars, as those weapons should be under the command of the platoon leader who is directing the assault over the last 100-200 m.

Suppressive fires have been found to be superior to destructive fires against protected positions. It's a combined arms tactics thing, supported by military historical research and operational research.

There are some armies -typically with a tradition of lavish wartime production- that overemphasize destructive fires against protected targets, of course.

This relative importance of suppression is part of the reason why destructiveness against protected targets should be rated lowly as a indirect fire requirement.

For starters check FM 7-90: "Mortars allow the maneuver commander to quickly place *killing* indirect fires on the enemy" "suppressive *and* destructive effects" "mortar fire acts *both* as a killer of enemy forces and as an enhancer of friendly mobility"

More interesting stuff up to come as soon as you start citing evidence instead of unqualified oppinions.

Well, I grant you that I wrote once about destructive fires without specifying that I meant them against protected targets, but I was more specific another time."Their utility in destroying protected targets is marginal.""...destructiveness against protected targets should be rated lowly as a indirect fire requirement. "

Your quote does therefore not provide any relevant evidence here.

On the other hand, throwing info is surely better than throwing opinion...

The ammunition for destructive fire (which is of course not even close to 100% destructiveness) against covered soft targets equals thus* 100-120 sec suppressive firesor* more than 7 minutes of smoke on target.You need at least 30 sec suppression after the "destructive" fires because those were not 100% destructive...which tilts the whole calculation very much in favour of suppression.

This is clearly about ammo quantities that are not acceptable for porter logistics. 120x 81mm mortar bombs with charges weigh about 500 kg + cases!This was - while about more than a single field bunker - only about defeating a much smaller opposition than a Bn equivalent.

The same source offers a typical fires plan for an infantry battalion in the defence; 650 planned shots 81 and 120 mm + unpredicted quantities for the main fire mission.An attacking battalion cannot hope to come even close to this firepower with porter logistics, thus the need for longer-ranged mortars than 81.4mm.

That Russian 107mm mountain mortar had 160 kg weight, one axle and 6100 m range already back in '38 - vastly superior to contemporary 81.4mm, but it required about the same crew.

A relatively popular book that offers more about destructive vs. suppressive fires is "On artillery" by B.I.Gudmundsson.More here: http://nigelef.tripod.com/wt_of_fire.htm

Why should anyone bother to shell 4 hectare to destroy a target of 2 by 2 m? The propable error (the area hit by 50% of the rounds fired) of a 81mm mortar is (range x bearing) 5x3 m at 500 m, 9x3 m at 1000 m, and 15x6 m at 2000 m!

It clearly shows the drawbacks that come with the employment of mortars as a battery weapon. With greater range, accuracy is compromised, with greater distance between firing and observation positions friction hampers rapid fire corrections; contact with the infantry weakens and therefore proper target identification is lacking; ergo mortars began to emulate artillery firing methods.

This is not an overall bad process* (for 120mm mortars, to use 81mm mortars consistently that way is propably misuse). Today immediate destructive fires at selective enemy targets can be delivered by other weapon systems (tanks, MICV, ATGM etc.). Radio and fire direction computers have speeded and eased up the fire direction process. But, this was not the case in the period of the world wars. In those days mortar teams and squads crept up just behind the infantry (HDv 130/9, Nr. 65, 70 and below) to deliver mostly destructive fires against enemy positions that tried to stop the infantrys approach. The unit of fire was the mortar team (HDv 130/9, Nr. 12). In 1944 the mortar squad became the main unit of fire (Merkblatt 25b/32) propably first of all because of the lack of trained personell. The employment of platoon fires from one position was rather rare. Mortar fire was part of a system of fires and did not just engage any target that showed itself in their range. They engaged only selected targets in order to archive a certain tactical aim. Area fire was assigned to medium machine guns and artillery.

*) most of all ammunition supply becomes easy as you propably can drive to the firing position by truck.

MkBl 25b/32 on destructive fires:"immobile point targets are to be destroyed (zerstört), after zeroing in, by concentrated fire of one or several Squads, frequently by lone mortars.Point targets, that are able to evade the mortar fire easily, are to be engaged (bekämpft - obviously this implicates the intend of destroying them, as in the paragraph above, see Feuerüberfall), after approximately zeroing in on the target itself or a aid-target (Einschießziel), by supprise high volume fire (Feuerüberfall)."The following paragraph treads the engagement (Bekämpfung) of large targets such as moving infantry, enemy troops in being, or accumulation of enemy troops. Obviously none of the targets given as example would be engaged with the intention of suppressing them. Actually the term suppression (niederhalten) does not even appear in the whole manual.An optimal disposition would be the observation post roughly on the line drawn between firing position and target, with visual contact to firing position, aiming point and target. This allowed for the most simple fire direction procedure, as the observer could establish bearing simply by means of his field glasses.

HDv 130/9, Nr. 73"The heavy [81mm] mortars, from firing position in the combat zone of the infantry companies, subdue (niederkämpfen - in Wehrmacht-terminology this usually means that fire has to destroy the enemy in time, if he does not choose to evade the fire) the enemy in positions (Deckung), visible only for short times, according to the orders of the company leaders."

Both manuals are wartime publications, first issued in 1941 and 1944 respectively.

To substanciate my claim about direct fire of IGs:HDv 130/4 Nr. 162"The firing position has to be out of view of the enemy and offer good effect of fire in the target area assigned"Nr. 103"Fire from open positions is to be confined to exeptionaly situations."In the tactical discussion of IG employment direct fire is mentioned only twice. First in MOUT, second as a stop gap tank defence of halts.

About the whole point target thing; look at WW2 fortification patterns and you'll see that they are no point targets unless you speak about a Grand Slam bomb. The size of a squad fortification was easily 50 x 20 m. The more common platoon strongpoints were larger. It doesn't help to knock out a point target if the defenders can dodge your fire with movement in trenches.

There's also the issue of navigation. Especially the wide open plains of the Ukraine and North Africa were terrible for navigation by triangulation. Moving the impacts on the target (with safety distance to own troops!) was difficult under such conditions. It costed much ammo and time. This reduces the relative difference between point and area target engagement.There's also the issue of decoy positions and undetected positions. To fire at the area of a hedgehog position was simply better.

In short: Suppressive and smoke fires on the area of a hedgehog position, accurate fires (often with observer in shouting distance to mortar crew, as on a ridge) against small and exposed teams (such as for securing a patrol, for example) and prepared rapid destructive area fires to break up assaults.

HDv sources about direct fire represent theory; I described the wartime employment of IGs in defensive company strongpoints.

Aha, there were no AT-guns, no machine gun nests, no observation posts ...

Even a squad position is a much smaller target area than 200 x 200 m with much less rounds to be fired for destructive effect. Allthough such a position would propably not one of those essential targets preferably engaged by mortar destructive fires. A squad position would propably come under mortar fire in support of am assault in the time after the lift of artillery fires.

artillery methods were not used for fire direction of mortars. As I mentioned a outstandig terrain feature (lone tree, edge of a wood, a church tower etc) were used for general direction with aiming stakes on the frontal cover to transmit the direction to the firing position. The observation post would preferably be on or near this line.

Doctrine at least by 1944 should have cought up to what actually happened and was usefull in the field. Especially so on a rather simply question of if field commanders employed mortars in platoons or squads. For example the unit of fire was changed from mortar team to mortar squad, propably becaus the wehrmacht lacked properly trained mortar leaders. If you described the use of IGs, you propably gave us your own misconceptions, as you have obviously no idea of the underlying doctrine (prove me wrong).

There's still a difference between doctrine ('what is being taught and written in manuals') and what's being done.

In the case of defence, infantry guns were regularly included in company strongpoints for direct fire purposes since there was usually no other or not enough other direct fire guns available. 75 mm HE shells negate much more cover than a 7.92 mm machine gun - an important ability even in the tactical defence.By the way; even the relatively huge 105 mm guns were at times brought forward for direct fire, even on the attack.

It doesn't take much reading to stumble upon examples.

You should also take note that mortar were very important for fighting in woods. There was no choice but to use artillery-like techniques for their employment in woods, and the German army did learn to use mortars to good effect in woods during 1941/42, in part due to contact with the Finns.Good mortar teams had arty-like techniques in their repertoire.